U.S. patent number 7,580,329 [Application Number 11/339,759] was granted by the patent office on 2009-08-25 for optical recording medium recorded with information in depth direction, and method and apparatus of reproduction therefrom.
This patent grant is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Junsaku Nakajima, Masaru Nomura, Kenji Ohta, Hitoshi Takeuchi.
United States Patent |
7,580,329 |
Nakajima , et al. |
August 25, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Optical recording medium recorded with information in depth
direction, and method and apparatus of reproduction therefrom
Abstract
An optical disk has a lead-in region provided at the inner
circumference side and a user region provided at the outer
circumference side. Pit string 3 of pits of different depths is
formed in the lead in region. Light beam reflected from the pit
string is detected by detector and TPP and RF signals are output by
differential amplifier and addition amplifier. A ternary signal is
restored from pits based on the TPP and RF signals. Information is
recorded by pits of the same depth in the user region. Recording
information in the depth direction in the lead-in region increases
the recording capacity thereof. The information recorded in the
depth direction in the lead-in region cannot be transferred to a
user region of another optical disk.
Inventors: |
Nakajima; Junsaku (Kashihara,
JP), Takeuchi; Hitoshi (Kitakatsuragi-Gun,
JP), Nomura; Masaru (Nabari, JP), Ohta;
Kenji (Kitakatsuragi-Gun, JP) |
Assignee: |
Sharp Kabushiki Kaisha (Osaka,
JP)
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Family
ID: |
18616029 |
Appl.
No.: |
11/339,759 |
Filed: |
January 24, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070177489 A1 |
Aug 2, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09824554 |
Apr 2, 2001 |
7050383 |
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Foreign Application Priority Data
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Apr 4, 2000 [JP] |
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2000-102088 |
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Current U.S.
Class: |
369/44.26;
369/47.1 |
Current CPC
Class: |
G11B
7/005 (20130101); G11B 7/007 (20130101); G11B
7/24085 (20130101); G11B 20/00086 (20130101); G11B
20/00688 (20130101) |
Current International
Class: |
G11B
7/00 (20060101) |
Field of
Search: |
;369/275.3,44.41,53.22,44.26,47.27,275.2,47.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2085974 |
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4403171 |
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Aug 1995 |
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DE |
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05-42730 |
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May 1993 |
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EP |
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0542730 |
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May 1993 |
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EP |
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05-45472 |
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Jun 1993 |
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EP |
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0545472 |
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Jun 1993 |
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EP |
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07-08439 |
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Apr 1996 |
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EP |
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0708439 |
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Apr 1996 |
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EP |
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09-05683 |
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Mar 1999 |
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EP |
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0905683 |
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Mar 1999 |
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EP |
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44-03171 |
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Aug 1999 |
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EP |
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10-67523 |
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Jan 2001 |
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EP |
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60-242532 |
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Dec 1985 |
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JP |
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03-141032 |
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Jun 1991 |
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JP |
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05-205276 |
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Aug 1993 |
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JP |
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05-290379 |
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Nov 1993 |
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JP |
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06-215380 |
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Aug 1994 |
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JP |
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07-272282 |
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Oct 1995 |
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JP |
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08-153331 |
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Jun 1996 |
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JP |
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10-106042 |
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Apr 1998 |
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JP |
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2000-048478 |
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Feb 2000 |
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JP |
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2001-076347 |
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Mar 2001 |
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JP |
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WO-99-13466 |
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Mar 1999 |
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WO |
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WO-99/13466 |
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Mar 1999 |
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WO |
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Other References
US. Appl. No. 09/606,282, filed Jun. 29, 2000, Junsaku Nakajima, et
al. cited by other.
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Primary Examiner: Hindi; Nabil Z
Attorney, Agent or Firm: Edwards Angell Palmer & Dodge
LLP Conlin; David G. Tucker; David A.
Parent Case Text
This is a divisional patent application of U.S. patent application
Ser. No. 09/824,554 filed 2 Apr. 2001, by the same inventors as of
this divisional application, entitled "OPTICAL RECORDING MEDIUM
RECORDED WITH INFORMATION IN DEPTH DIRECTION, AND METHOD AND
APPARATUS OF REPRODUCTION THEREFROM.
Claims
What is claimed is:
1. A reproduction method of an optical recording medium recorded
with information on a substrate, said optical recording medium
including a first region having first information recorded at least
in a depth direction of said substrate by pits of at least two
different depths formed on said substrate, and a second region
having second information recorded in a plane direction of said
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on said substrate, said
reproduction method comprising the steps of: reproducing said first
information in said first region based on a polarity of a
tangential push-pull signal obtained from said pits, said polarity
differing according to the depth of a pit, and reproducing said
second information in said second region based on a signal
representing a quantity of reflected light obtained from said
pit.
2. A reproduction method of an optical recording medium recorded
with information on a substrate, said optical recording medium
including a first region having first information recorded at least
in a depth direction of said substrate by pits of at least two
different depths formed on said substrate, and a second region
having second information recorded in a plane direction of said
substrate by at least one of the absence/presence, the length, the
width and the position of a pit formed on said substrate, said
reproduction method comprising the steps of: reproducing said first
information in said first region based on a signal representing a
quantity of reflected light obtained from said pit and a polarity
of a tangential push-pull signal obtained from said pits, said
polarity differing according to the depth of a pit, and reproducing
said second information in said second region based on said signal
representing the quantity of reflected light obtained from said
pit.
3. A reproduction apparatus of an optical recording medium recorded
with information on a substrate, said optical recording medium
including a first region having first information recorded at least
in a depth direction of said substrate by pits of at least two
different depths formed on said substrate, and a second region
having second information recorded in a plane direction of said
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on said substrate, said
reproduction apparatus comprising: a circuit reproducing said first
information in said first region based on a polarity of a
tangential push-pull signal obtained from said pits, said polarity
differing according to the depth of a pit, and a circuit
reproducing said second information in said second region based on
a signal representing the quantity of reflected light obtained from
said pit.
4. A reproduction apparatus of an optical recording medium recorded
with information on a substrate, said optical recording medium
including a first region having first information recorded at least
in a depth direction of said substrate by pits of at least two
different depths formed on said substrate, and a second region
having second information recorded in a plane direction of said
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on said substrate, said
reproduction apparatus comprising: a circuit reproducing said first
information in said first region based on a signal representing a
quantity of reflected light obtained from said pit, and a polarity
of a tangential push-pull signal obtained from said pits, said
polarity differing according to the depth of a pit, and a circuit
reproducing said second information in said second region based on
said signal representing the quantity of reflected light obtained
from said pit.
5. A reproduction method of an optical recording medium that can
have information recorded on a substrate, said optical recording
medium including a first region having first information recorded
at least in a depth direction of said substrate by pits of at least
two different depths formed on said substrate, and a second region
that can have second information recorded in a plane direction of
said substrate by at least one of the presence/absence, the length,
the width and the position of a mark formed on said substrate, said
reproduction method comprising the steps of: reproducing said first
information in said first region based on a polarity of a
tangential push-pull signal obtained from said pits, said polarity
differing according to the depth of a pit, and reproducing said
second information in said second region based on a signal
representing a quantity of reflected light obtained from said
mark.
6. A reproduction method of an optical recording medium that can
have information recorded on a substrate, said optical recording
medium including a first region having first information recorded
at least in a depth direction of said substrate by pits of at least
two different depths formed on said substrate, and a second region
that can have second information recorded in a plane direction of
said substrate by at least one of the absence/presence, the length,
the width and the position of a mark formed on said substrate, said
reproduction method comprising the steps of: reproducing said first
information in said first region based on a signal representing a
quantity of reflected light obtained from said pit and a polarity
of a tangential push-pull signal obtained from said pits, said
polarity differing according to the depth of a pit, and reproducing
said second information in said second region based on said signal
representing the quantity of reflected light obtained from said
mark.
7. A reproduction apparatus of an optical recording medium that can
have information recorded on a substrate, said optical recording
medium including a first region having first information recorded
at least in a depth direction of said substrate by pits of at least
two different depths formed on said substrate, and a second region
that can have second information recorded in a plane direction of
said substrate by at least one of the presence/absence, the length,
the width and the position of a mark formed on said substrate, said
reproduction apparatus comprising: a circuit reproducing said first
information in said first region based on a polarity of a
tangential push-pull signal obtained from said pits, said polarity
differing according to the depth of a pit, and a circuit
reproducing said second information in said second region based on
a signal representing the quantity of reflected light obtained from
said mark.
8. A reproduction apparatus of an optical recording medium that can
have information recorded on a substrate, said optical recording
medium including a first region having first information recorded
at least in a depth direction of said substrate by pits of at least
two different depths formed on said substrate, and a second region
that can have second information recorded in a plane direction of
said substrate by at least one of the presence/absence, the length,
the width and the position of a mark formed on said substrate, said
reproduction apparatus comprising: a circuit reproducing said first
information in said first region based on a signal representing a
quantity of reflected light obtained from said pit and a polarity
of a tangential push-pull signal obtained from said pits, said
polarity differing according to the depth of a pit and a circuit
reproducing said second information in said second region based on
said signal representing the quantity of reflected light obtained
from said mark.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium in
which information is recorded in the direction of depth of the
substrate, and a method and apparatus of reproducing information
therefrom. More particularly, the present invention relates to a
read only or recordable optical recording medium including a first
region in which first information such as additional information is
recorded at least in the depth direction of the substrate and a
second region in which second information such as main information
is recorded or can be recorded in the plane direction of the
substrate, and a reproduction method and reproduction apparatus of
such an optical recording medium.
2. Description of the Background Art
In a conventional optical recording medium such as an optical disk,
binary recording is carried out, wherein information is binarized
and recorded corresponding to the presence/absence, the length, the
width, or the position in the substrate plane of pits, marks and
the like. More specifically, pits are provided on the substrate in
a read only optical disk (referred to as ROM disk hereinafter) to
have information recorded. In contrast, recording marks are
provided at the recording layer on the substrate in a recordable
disk such as a phase change disk, magneto-optical disk, and organic
dye disk to have information recorded.
Information is transposed to the absence/presence, the length, the
width, or the position in-the substrate plane of pits, marks or the
like to be recorded on an optical disk. In other words, information
is recorded in the dimension of the plane direction of the
substrate using pits, marks and the like. The string of pits,
marks, or the like is arranged concentrically or spirally on a
circular substrate to form a track. The light beam for reproduction
follows this track to scan the string of pits, marks or the like.
Taking advantage of the change in the quantity of reflected light,
rotation of the plane of polarization of light and the like based
on these pits and marks, recorded information is reproduced.
The pit string, mark string and the like formed concentrically or
spirally are generally assigned an address sequentially from the
inner circumference towards the outer circumference. A
predetermined region at the inner circumference side with the
smaller address constitutes the region generally called "lead-in".
Information unique to the relevant optical disk is written in this
lead-in region. More specifically, various information required for
the disk drive, disk player, disk recorder or the like to record
information or reproduce information to/from the optical disk is
written in the lead-in region.
Information unique to the disk includes, for example, information
identifying the disk type (ROM disk, R disk, RW disk, RAM disk, or
the like), information specifying the rotation speed and linear
velocity of the disk for recording and reproduction, the laser
power during recording or the like, the address information of a
region on the disk that can be used by the user, key information
required to cancel the scramble or encryption, and the like.
The key required to descramble or decrypt is the key used in
scrambling or encrypting the contents. The scramble or encryption
cannot be canceled without this key. In other words, this release
key is indispensable to reproduce the scrambled or encrypted
contents.
In accordance with the higher density and higher level of functions
of disks, the trend is to increase the amount of information
written in the lead-in region.
A conventional optical recording medium and a reproduction method
and apparatus of an optical recording medium will be described
hereinafter with reference to the drawings.
FIGS. 6-8 show a first example of a conventional optical recording
medium. FIG. 6 schematically shows the arrangement of pits formed
on a ROM disk as an example of an optical recording medium. A pit
string 33 of a plurality of pits 32 are formed spirally on the
plane of a substrate 31, whereby information is recorded.
FIG. 7A is a schematic representation of pit string 33 formed
spirally in the conventional ROM disk of FIG. 6, illustrated in a
linear version from the inner circumference region to the outer
circumference region of substrate 31. The lead-in region is
provided at the inner circumference side of the disk, and the user
region is provided at its outer circumference side.
The ROM disk ID (identification information), the address
information of the user region and the like are recorded in the
lead-in region. When the information written in the user region is
scrambled or encrypted, a scramble key or encryption key thereof is
also recorded in this lead-in region.
Main information such as video and audio data is recorded in the
user region. When the contents become the subject of copyright
protection, the main information will be recorded in a scrambled or
encrypted manner.
FIG. 7B is a schematic sectional representation of substrate 31
corresponding to pit string 33 of FIG. 7A. The portion of pit 32 is
represented as a hole. Pit 32 is formed with a constant depth.
FIG. 7C shows an RF signal representing the quantity of reflected
light obtained by reproducing pit string 33 with a reproduction
light beam (not shown). FIG. 7D represents a tangential push-pull
signal (TPP signal) obtained by reproducing pit string 33.
The RF signal and TPP signal will be described hereinafter with
reference to FIGS. 7C, 7D and FIGS. 8A and 8B. FIG. 8A
schematically shows the scanning manner of a beam spot 34 of the
light beam for reproduction on pit 32. FIG. 8B schematically shows
the manner of reflected light 35 of the reproduction light beam
from the disk plane entering photoreceptor elements 36a and 36b
forming a detector 37 that is divided into two regions, region A
and region B. The RF signal and TPP signal are obtained by the
following equations using respective outputs A and B of
photoreceptor elements 36a and 36b. RF=A+B TPP=A-B
An RF signal having a waveform as shown in FIG. 7C is obtained
since the quantity of reflected light of the light beam is small at
the pit portion and large at the non-pit portion. Also, since the
pit is formed with a constant depth, a TPP signal as shown in FIG.
7D that changes with the same polarity will be obtained with
respect to all pits, as will be described afterwards.
FIGS. 11A and 11B schematically show a structure of a string of
marks in a recordable disk which is a second example of a
conventional optical recording medium. FIGS. 11C and 11D represent
the waveforms of respective signals obtained by reproducing
information from the recordable disk.
FIG. 11A schematically shows a mark string 46 formed of a number of
marks 45 written on the plane of a recordable disk, illustrated in
a linear version from the inner circumference region to the outer
circumference region of a substrate 41. A guide groove of the light
beam that is generally referred to as a groove is provided in the
recordable disk. The light beam for recording follows this groove
44 or the land which is a region between grooves to write a mark
45. Mark 45 can be written in either or both of the groove and
land. FIG. 11A shows an example of marks 45 written in groove
44.
FIG. 11B schematically shows a cross section of the disk,
corresponding to mark string 46 of FIG. 11A. It is appreciated from
FIG. 11B that the mark portion is provided so that the reflectance
of light differs between a mark portion 45 and a non-mark portion
48 in a recording layer 47 provided on substrate 41, and not formed
as a hole such as for the pit.
FIG. 11C shows an RF signal representing the quantity of reflected
light obtained by reproducing mark string 46 with a reproduction
light beam. The quantity of reflected light is smaller in mark
portion 45 than in non-mark portion 48.
FIG. 11D represents a TPP signal obtained by reproducing mark
string 46. Since mark 45 is formed with a constant depth in groove
44, a TPP signal that changes with the same polarity is obtained
from all marks 45.
FIGS. 12 and 13A-13D show a third example of a conventional optical
recording medium. FIG. 12 schematically shows a recordable disk
that employs a phase change recording layer in an unrecorded status
as an example of an optical recording medium. A groove 54 which is
a guide groove is formed spirally on the plane of a substrate 51.
Information is recorded in the form of marks in groove 54. Pits 52
are formed instead of groove 54 at the inner circumference side of
the disk. Information that should not be rewritten is recorded by
pits 52.
FIGS. 13A and 13B schematically show the structure of a mark string
and pit string of the recordable disk of FIG. 12. FIGS. 13C and 13D
represent the waveforms of respective signals obtained by
reproducing recorded information from the recordable disk.
FIG. 13A schematically shows a mark string 56 formed of marks 55
recorded on a spiral groove 54 and a pit string 53 formed of pits
52 in the recordable disk, illustrated in a linear version from the
inner circumference region to the outer circumference region of
substrate 51. It is to be particularly noted that marks 53 and pits
52 are aligned in the lead-in region.
Mark 55 can be written in either or both of the groove and land. In
the example of FIG. 13A, marks 55 are written in groove 54. The
lead-in region is provided at the inner circumference side of the
disk, and the user region is provided at its outer circumference
side. In the lead-in region, recorded are the disk ID
(identification information), the address information of the user
region, and the scramble key or encryption key in the case where
the information written in the user region is scrambled or
encrypted.
The user region is recorded with main information such as video and
audio data. When the contents are copyrighted, the main information
is recorded in a scrambled or encrypted manner.
FIG. 13B schematically shows the cross section of the disk
corresponding to mark string 56 and pit string 53 of FIG. 13A. Pit
52 is formed as a hole with a constant depth. In contrast to the
formation of a hole as for pit 52, mark 55 is provided so that the
reflectance of light differs between a mark portion 55 and a
non-mark portion 58 in a recording layer 57 provided on substrate
51.
Although the depths of groove 54 and pit 52 may be identical, it is
preferable for a shallower groove 54 for the purpose of improving
the signal quality of mark 55. If the signal quality of pit 52 is
to be set more favorable, a depth of approximately .lamda./4n is
preferable, as will be described afterwards. Therefore, it is
preferable to form the pit deeper than the groove. Here, .lamda. is
the wavelength of light, and n is the refractive index of the disk
substrate.
FIG. 13C shows an RF signal representing the quantity of reflected
light obtained by reproducing mark string 56 and pit string 53 with
a reproduction light beam. FIG. 13C corresponds to the case where
the reflectance of mark portion 55 is smaller than the reflectance
of non-mark portion 58.
FIG. 13D represents a TPP signal obtained by reproducing mark
string 56 and pit string 53. Since mark 55 in groove 54 as well as
pit 52 are formed with the same constant depth, a TPP signal that
changes with the same polarity can be obtained from any mark and
pit.
In the present third conventional example, the relationship between
pit 52 and the beam spot is similar to that of the first
conventional example shown in FIGS. 8A and 8B. Therefore, the RF
signal and TPP signal are obtained by the following equations using
respective outputs A and B of photoreceptor elements 36a and 36b of
detector 37. RF=A+B TPP=A-B
An RF signal as shown in FIG. 13C is obtained since the quantity of
reflected light of the light beam is small at the pit portion and
large at the non-pit portion whereas the reflectance is small at
the mark portion and large at the non-mark portion. Referring to
FIG. 13D, a TPP signal that changes at the same polarity from any
pit can be obtained as will be described afterwards since pits 52
are formed with the constant depth. The TPP signal obtained from
the mark portion and the TPP signal obtained from the pit portion
have the same polarity.
In the above-described conventional ROM disk, a greater capacity
(larger region) is required for the lead-in region as the amount of
information written in the lead-in region increases. There was a
problem that the region where user data can be recorded on the disk
is reduced. Similarly in the above-described conventional
recordable disk, a greater capacity larger region) is required for
the lead-in region as the amount of information written in the
lead-in region increases. There was a problem that the region where
the user can write data on the disk is reduced.
From the standpoint of copyright protection, it is not desirable
for the information in a ROM disk recorded with copyrighted
contents to be easily copied to another recordable disk. However,
since the conventional ROM disk has information recorded in the
dimension of the plane direction of the substrate using pits, it is
theoretically possible to copy the information in a ROM disk to
another recordable disk. The role of copyright protection is low.
Similarly in a conventional recordable disk, information in the
recordable disk can be easily copied to another recordable disk in
theory since information is recorded in the dimension of the plane
direction of the substrate using pits, marks, and the like. The
role of copyright protection is low.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical
recording medium and a reproduction method and apparatus thereof
that allows the capacity of the lead-in region to be increased
while reserving sufficient region for usage by a user without
enlarging the lead-in region.
Another object of the present invention is to provide an optical
recording medium and a reproduction method and apparatus thereof
that can prevent copying of a read only disk or recordable disk
that is recorded with copyrighted contents.
According to an aspect of the present invention, an optical
recording medium recorded with information on a substrate includes
a first region having first information recorded at least in a
depth direction of a plane direction and depth direction of the
substrate, and a second region having second information recorded
in the plane direction of the substrate.
According to the present invention, more information can be
recorded in the first region since the recording density can be
increased in the first region where information is recorded in the
depth direction as compared with a convention optical recording
medium.
Since the first information in the first region is recorded in the
depth direction, copying to another recordable medium that records
information in the plane direction can be prevented.
According to another aspect of the present invention, a
reproduction method of an optical recording medium recorded with
information on a substrate is provided. The optical recording
medium includes a first region having first information recorded at
least in the depth direction of the substrate by pits of at least
two different depths formed on the substrate, and a second region
having second information recorded in a plane direction of the
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on the substrate. The
reproduction method of an optical recording medium includes the
steps of reproducing the first information in the first region
based on a polarity of a tangential push-pull signal obtained from
the pits, the polarity differing according to the depth of a pit,
and reproducing the second information in the second region based
on a signal representing a quantity of reflected light obtained
from the pit.
Since the first information is reproduced based on a tangential
push-pull signal in the present invention, multivalued information
can now be reproduced that was not possible by the conventional
reproduction method that reproduces binary information based on
only a signal representing the quantity of reflected light. Also,
since the second information is reproduced based on a signal
representing the quantity of reflected light in the second region,
a conventional reproduction circuit can be used for the
reproduction circuit of this region. Accordingly, the cost of the
reproduction apparatus can be reduced.
According to a further aspect of the present invention, a
reproduction method of a optical recording medium recorded with
information on a substrate is provided. The optical recording
medium includes a first region having first information recorded at
least in a depth direction of the substrate by pits of at least two
different depths formed on the substrate, and a second region
having second information recorded in a plane direction of the
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on the substrate. The
reproduction method of an optical recording medium includes the
steps of reproducing the first information in the first region
based on a signal representing a quantity of reflected light
obtained from the pit and a polarity of a tangential push-pull
signal obtained from the pits, the polarity differing according to
the depth of a pit, and reproducing second information in the
second region based on the signal representing the quantity of
reflected light obtained from the pit.
Since the first information is reproduced based on a signal
representing the quantity of reflected light obtained from a pit
and a tangential push-pull signal in the present invention,
multivalued information can now be reproduced that was not possible
by the conventional reproduction method that reproduces binary
information based on only a signal representing the quantity of
reflected light. Also, since the second information is reproduced
based on a signal representing the quantity of reflected light in
the second region, a conventional reproduction-circuit can be used
for the reproduction circuit of this region. Accordingly, the cost
of the reproduction apparatus can be reduced.
According to still another aspect of the present invention, a
reproduction apparatus of an optical recording medium recorded with
information on a substrate is provided. The optical recording
medium includes a first region having first information recorded at
least in a depth direction of the substrate by pits of at least two
different depths formed on the substrate, and a second region
having second information recorded in a plane direction of the
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on the substrate. The
reproduction apparatus of the optical recording medium includes a
circuit reproducing the first information in the first region based
on a polarity of a tangential push-pull signal obtained from the
pits, the polarity differing according to the depth of a pit, and a
circuit reproducing the second information in the second region
based on a signal representing the quantity of reflected light
obtained from the pit.
Since the first information is reproduced based on a tangential
push-pull signal in the present invention, multivalued information
can now be reproduced that was not possible by the conventional
reproduction apparatus that reproduces binary information based on
only a signal representing the quantity of reflected light. Also,
since the second information is reproduced based on a signal
representing the quantity of reflected light in the second region,
a conventional reproduction circuit can be used for the
reproduction circuit of this region. Accordingly, the cost of the
reproduction apparatus can be reduced.
According to a still further aspect of the present invention, a
reproduction apparatus of an optical recording medium recorded with
information on a substrate is provided. The optical recording
medium includes a first region having first information recorded in
at least in a depth direction of the substrate by pits of at least
two different depths formed on the substrate, and a second region
having second information recorded in a plane direction of the
substrate by at least one of the presence/absence, the length, the
width and the position of a pit formed on the substrate. The
reproduction apparatus of the optical recording medium includes a
circuit reproducing the first information in the first region based
on a signal representing a quantity of reflected light obtained
from the pit, and a polarity of a tangential push-pull signal
obtained from the pits, the polarity differing according to the
depth of a pit, and a circuit reproducing the second information in
the second region based on the signal representing the quantity of
reflected light obtained from the pit.
Since the first information is reproduced based on a signal
representing the quantity of reflected light obtained from a pit
and a tangential push-pull signal in the present invention,
multivalued information can now be reproduced that was not possible
by the conventional reproduction apparatus that reproduces binary
information based on only a signal representing the quantity of
reflected light. Also, since the second information is reproduced
based on a signal representing the quantity of reflected light in
the second region, a conventional reproduction circuit can be used
for the reproduction circuit of this region. Accordingly, the cost
of the reproduction apparatus can be reduced.
According to yet a further aspect of the present invention, a
recorded information identification method of an optical recording
medium recorded with information on a substrate is provided. The
optical recording medium includes a region in which the presence of
pits of at least two different depths formed on the substrate
indicates identification information that is unique to the optical
recording medium. The recorded information identification method
includes the steps of detecting a polarity of a tangential
push-pull signal obtained from the pits, the polarity differing
according to the depth of a pit, and identifying the unique
identification information based on the detected polarity.
In an optical recording medium in which the presence of pits of
different depths indicates identification information that is
unique to that optical recording medium of the present invention,
the optical recording medium is identified based on the polarity of
the tangential push-pull signal obtained from the pits. Therefore,
the optical recording medium can be identified reliably.
According to yet another aspect of the present invention, a
recorded information identification apparatus of an optical
recording medium recorded with information on a substrate is
provided. The optical recording medium includes a region in which
the presence of pits having at least two different depths formed on
the substrate indicates identification information that is unique
to the optical recording medium. The recorded information
identification apparatus includes a circuit detecting a polarity of
a tangential push-pull signal obtained from the pits, the polarity
differing according to the depth of a pit, and a circuit
identifying the unique identification information based on the
detected polarity.
In an optical recording medium in which the presence of pits of
different depths indicates identification information that is
unique to the optical recording medium of the present invention,
the optical recording medium is identified based on the polarity of
the tangential push-pull signal obtained from the pits. Therefore,
the optical recording medium can be identified reliably.
According to yet a still further aspect of the present invention,
an optical recording medium that can have information recorded on a
substrate includes a first region having first information recorded
at least in a depth direction of a plane direction and depth
direction of the substrate, and a second region than can have
second information recorded in the plane direction of the
substrate.
According to the present invention, more information can be
recorded in the first region since the recording density can be
increased in the first region where information is recorded in the
depth direction as compared with a convention optical recording
medium.
Since the first information in the first region is recorded in the
depth direction, copying to another recordable medium that records
information in the plane direction can be prevented.
According to an additional aspect of the present invention, a
reproduction method of an optical recording medium that can have
information recorded on a substrate is provided. The optical
recording in medium includes a first region having first
information recorded at least in a depth direction of the substrate
by pits of at least two different depths formed on the substrate,
and a second region that can have second information recorded in a
plane direction of the substrate by at least one of the
presence/absence, the length, the width and the position of a mark
formed on the substrate. The reproduction method of an optical
recording medium includes the steps of reproducing the first
information in the first region based on a polarity of a tangential
push-pull signal obtained from the pits, the polarity differing
according to the depth of a pit, and reproducing the second
information in the second region based on a signal representing a
quantity of reflected light obtained from the mark.
Since the first information is reproduced based on a tangential
push-pull signal in the present invention, multivalued information
can now be reproduced that was not possible by the conventional
reproduction method that reproduces binary information based on
only a signal representing the quantity of reflected light. Also,
since the second information is reproduced based on a signal
representing the quantity of reflected light from a mark in the
second region, a conventional reproduction circuit can be used for
the reproduction circuit of this region. Accordingly, the cost of
the reproduction apparatus can be reduced.
According to another aspect of the present invention, a
reproduction method of an optical recording medium that can have
information recorded on a substrate is provided. The optical
recording medium includes a first region having first information
recorded at least in a depth direction of the substrate by pits of
at least two different depths formed on the substrate, and a second
region that can have second information recorded in a plane
direction of the substrate by at least one of the presence/absence,
the length, the width and the position of a mark formed on the
substrate. The reproduction method of an optical recording medium
includes the steps of reproducing the first information in the
first region based on a signal representing a quantity of reflected
light obtained from the pit and a polarity of a tangential
push-pull signal obtained from the pits, the polarity differing
according to the depth of a pit, and reproducing the second
information in the second region based on the signal representing
the quantity of reflected light obtained from a mark.
Since the first information is reproduced based on a signal
representing the quantity of reflected light obtained from a pit
and a tangential push-pull signal in the present invention,
multivalued information can now be reproduced that was not possible
by the conventional reproduction method that reproduces binary
information based on only a signal representing the quantity of
reflected light. Also, since the second information is reproduced
based on a signal representing the quantity of reflected light from
a mark in the second region, a conventional reproduction circuit
can be used for the reproduction circuit of this region.
Accordingly, the cost of the reproduction apparatus can be
reduced.
According to a further aspect of the present invention, a
reproduction apparatus of an optical recording medium that can have
information recorded on a substrate is provided. The optical
recording medium includes a first region having first information
recorded at least in a depth direction of the substrate by pits of
at least two different depths formed on the substrate, and a second
region that can have second information recorded in a plane
direction of the substrate by at least one of the absence/presence,
the length, the width and the position of a mark formed on the
substrate. The reproduction apparatus of the optical recording
medium includes a circuit reproducing the first information in the
first region based on a polarity of a tangential push-pull signal
obtained from the pits, the polarity differing according to the
depth of a pit, and a circuit reproducing the second information in
the second region based on a signal representing the quantity of
reflected light obtained from a mark.
Since the first information is reproduced based on a tangential
push-pull signal in the present invention, multivalued information
can now be reproduced that was not possible by the conventional
reproduction apparatus that reproduces binary information based on
only a signal representing the quantity of reflected light. Also,
since the second information is reproduced based on a signal
representing the quantity of reflected light in the second region,
a conventional reproduction circuit can be used for the
reproduction circuit of this region. Accordingly, the cost of the
reproduction apparatus can be reduced.
According to still another aspect of the present invention, a
reproduction apparatus of an optical recording medium that can have
information recorded on a substrate is provided. The optical
recording medium includes a first legion having first information
recorded at least in a depth direction of the substrate by pits of
at least two different depths formed on the substrate, and a second
region that can have second information recorded in a plane
direction of the substrate by at least one of the presence/absence,
the length, the width and the position of a mark formed on the
substrate. The reproduction apparatus of the optical recording
medium includes a circuit reproducing the first information in the
first region based on a signal representing a quantity of reflected
light obtained from the pit and a polarity of a tangential
push-pull signal obtained from the pits, the polarity differing
according to the depth of a pit, and a circuit reproducing the
second information in the second region based on the signal
representing the quantity of reflected light obtained from a
mark.
Since the first information is reproduced based on a signal
representing the quantity of reflected light from a pit and a
tangential push-pull signal in the present invention, multivalued
information can now be reproduced that was not possible by the
conventional reproduction apparatus that reproduces binary
information based on only a signal representing the quantity of
reflected light. Also, since the second information is reproduced
based on a signal representing the quantity of reflected light in
the second region, a conventional reproduction circuit can be used
for the reproduction circuit of this region. Accordingly, the cost
of the reproduction apparatus can be reduced.
The foregoing and other objects, features, aspects and advantages
of the present invention will become more apparent from the
following detailed description of the present invention when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1D schematically show the relationship between the
structure of an optical disk and signals obtained therefrom
according to a first embodiment of the present invention.
FIG. 2 is a block diagram representing a circuit configuration of
the main part of an optical disk reproduction apparatus according
to the first embodiment of the present invention.
FIG. 3 is a timing chart of the operation of the optical disk
reproduction apparatus according to the first embodiment of FIG.
2.
FIG. 4 is a block diagram representing a circuit configuration of
the main part of an optical disk reproduction apparatus according
to a second embodiment of the present invention.
FIGS. 5A-5D schematically show the relationship between the
structure of an optical disk and signals obtained therefrom
according to a third embodiment of the present invention.
FIG. 6 schematically shows the arrangement of pits formed on a
conventional ROM disk.
FIGS. 7A-7D schematically show the relationship between the
structure of a conventional optical disk of FIG. 6 and signals
obtained therefrom.
FIGS. 8A and 8B schematically show the manner of a light beam spot
running over a pit string and the manner of a detector receiving
reflected light of the light beam spot.
FIG. 9 is a graph representing the relationship among the pit
depth, TPP signal amplitude and RF signal amplitude.
FIG. 10 is a timing chart representing the relationship among the
pit depth, RF signal and TPP signal.
FIGS. 11A-11D schematically show the relationship between the
structure of an optical disk according to another conventional
example and signals obtained therefrom.
FIG. 12 is a schematic diagram showing a recordable disk of another
conventional example in an unrecorded state.
FIGS. 13A-13D schematically show the relationship between a
structure of a conventional optical disk of FIG. 12 and signals
obtained therefrom.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As previously described in the section of the related art, binary
recording is generally used that records information according to
the presence/absence, the length, the width, or the position in the
substrate plane of pits, marks, and the like in an optical disk.
However, information of larger capacity can be recorded if
information can be provided additionally in the depth direction of
the pit. Such a technique is already proposed in a copending U.S.
patent application Ser. No. 09/606282 by the inventors of the
present invention. The technique is directed to additionally
include information in the pit depth taking advantage of the fact
that the diffraction pattern caused by light interference generated
in a pit that has a recessed and protruded configuration differs
depending upon the pit depth.
FIG. 9 is a graph representing the relationship of the depth of,
for example, pit 32 shown in FIG. 8A with respect to the amplitudes
of an RF signal and TPP signal obtained therefrom. The depth of pit
32 is plotted along the horizontal axis with the wavelength .lamda.
of the light beam used for reproduction as the reference. In the
graph, n is the refractive index of the substrate of the optical
disk. In the present example, experiments are carried out as to an
optical disk including a transparent substrate having a thickness
of 0.6 mm and a refractive index of 1.5 using a reproduction light
beam of 650 nm in wavelength and an optical system having a
numerical aperture (NA) of 0.65.
Referring to FIG. 9, the amplitude of an RF signal exhibits the
maximum value when the pit depth is .lamda./4n (108 nm). The
vertical axis at the right side in FIG. 9 is a normalized amplitude
of the RF signal with 1 as the maximum value. The amplitude of the
TPP signal exhibits the maximum value when the pit depth is
.lamda./8n (54 nm). The vertical axis at the left side in FIG. 9 is
a normalized amplitude of the TPP signal with 1 as the maximum
value. The TPP signal has its polarity inverted at the border of
pit length .lamda./4n. To clearly show this inversion, the sign of
the TPP signal is set negative in the range of .lamda./4n (108
nm)<pit depth<.lamda./2n (216 nm).
The polarity inversion of the TPP signal will be described
hereinafter with reference to FIGS. 9 and 10. It is assumed that
pits 32a and 32b of FIG. 10 have a depth D1 (86 nm) and a depth D2
(130 nm), respectively. FIG. 10 represents the waveforms of the RF
signal and TPP signal obtained when a string of pits of such
different depths is reproduced. In FIG. 10, the light beam moves
from the left side to the right side. As shown in (a) of FIG. 10,
the RF signal exhibits a smaller quantity of reflected light in the
pit portion than in the non-pit portion in the pits of all depths.
As to pit 32a of depth D1, as shown in FIG. 10(b), the TPP signal
exhibits a pulse in the positive direction (upwards in FIG. 10) at
the leading edge of pit 32a, and then exhibits a pulse in the
negative direction (downwards in FIG. 10) at the trailing edge of
pit 32a. As to pit 32b of depth D2, the TPP signal exhibits a pulse
in the negative direction (downwards in FIG. 10) at the leading
edge of pit 32b and then a pulse in the positive direction (upwards
in FIG. 10) at the trailing edge of pit 32b. This phenomenon is
referred to as the inversion of the polarity of the TPP signal. In
FIG. 9, the polarity of the TPP signal obtained at pit 32a of depth
D1 is represented as positive and the opposite polarity of the TPP
signal is represented as negative.
Embodiments of the present invention will be described hereinafter
based on this polarity inversion of a TPP signal according to the
above-described different pit depth.
First Embodiment
An optical recording medium and a reproduction method and apparatus
thereof according to a first embodiment of the present invention
will be described hereinafter. FIGS. 1A and 1B schematically show a
structure of a pit string on a ROM disk as an example of an optical
recording medium in the first embodiment. FIGS. 1C and 1D represent
the waveforms of signals obtained by reproducing information from
the ROM disk.
More specifically, FIG. 1A schematically shows pit string 3
constituted by two types of pits 2a and 2b, illustrated in a linear
version from the inner circumference region to the outer
circumference region of the disk. FIG. 1B schematically shows the
cross section of the disk, corresponding to pit string 3 of FIG.
1A. Referring to FIG. 1B, the lead-in region is formed of
relatively shallow pits 2a (depth D1) and relatively deep pits 2b
(depth D2). The user region is formed of pits 2a of a constant
depth (depth D1). FIG. 1C shows an RF signal representing the
quantity of reflected light obtained by reproducing pit string 3
with a reproduction light beam. The quantity of reflected light is
smaller in the pit portion than in the non-pit portion. FIG. 1D
shows a TPP signal obtained by reproducing pit string 3 with the
reproduction light beam. As shown in FIG. 1B, the lead-in region is
formed of pits 2a and 2b that have depth differing from each other.
As described previously in relation to FIGS. 9 and 10, the polarity
of the obtained TPP signal is inverted between relatively shallow
pit 2a and relatively deep pit 2b. More specifically, by forming
the lead-in region with pits 2a and 2b of two different depths in
the first embodiment, information can be recorded in the depth
direction of the disk substrate taking advantage of the positive
and negative values that are easily determined as to the polarity
of the TPP signal.
These two pit depths (D1, D2) are to be set so that RF signals of
the same amplitude and TPP signals of different polarity are
obtained from pits 2a and 2b. More specifically, it will be
understood from the graph of FIG. 9 that the depths (D1, D2) are to
be set so as to satisfy: .lamda./8n<D1<.lamda./4n and
.lamda./4n<D2<3.lamda./8n where .lamda. is the wavelength of
the reproduction light beam and n is the refractive index of the
substrate.
The reproduction method and reproduction apparatus of information
recorded in a lead-in region formed of two different types of pits
2a and 2bhaving-different depths and in a user region formed of one
type of pits 2ahaving a constant depth will be described with
reference to FIGS. 2 and 3.
FIG. 2 is a schematic block diagram showing a circuit configuration
of the main part of a reproduction apparatus of the ROM disk shown
in FIG. 1. FIG. 3 is a timing chart representing the operation of
the reproduction apparatus of FIG. 2.
Description is based on the case where two types of pits 2a and 2b
arranged as shown in FIG. 3(a) are to be reproduced. It is assumed
that the depths of the pit are D1, D2 and D1 from left to right in
the example of FIG. 3.
Referring to FIG. 2, the outputs obtained from respective regions A
and B by directing reflected light 5 of reproduction beam spot from
the disk to regions A and B of a detector 6 are both provided to a
differential amplifier 7 and an addition amplifier 8. Differential
amplifier 7 obtains the difference between the outputs of regions A
and B of detector 6 to provide the difference as the TPP signal
shown in FIG. 3(c). Addition amplifier 8 obtains the total sum of
the outputs of regions A and B of detector 6 to provide the
obtained value as the RF signal of FIG. 3(b).
As to the RF signals indicating the quantity of reflected light of
the light beam (FIG. 3(b)), a correction process of the frequency
characteristics and the like is carried out by an equalization
circuit 12 on an RF signal reproduced from a pit of a particularly
short length. As shown in FIG. 3(d), the output of equalization
circuit 12 is binarized by a binarization circuit 13 and then
provided to a demodulation circuit not shown to be subjected to the
general demodulation process.
The TPP signal (FIG. 3(c)) is applied to both comparators 9 and 10.
Comparator 9 compares the input TPP signal with a preset positive
reference value. When the TPP signal is greater than the reference
value (i.e., the sign of the TPP signal is positive and the
absolute value thereof is great), one pulse (+1) is generated as
shown in FIG. 3(e) and provided to one input of an adder-subtracter
circuit 11. Similarly, comparator 10 compares the input TPP signal
with a preset negative reference value. When the TPP signal is
smaller than the reference value (i.e., the sign of the TPP signal
is negative and the absolute value thereof is large), one pulse
(-1) is generated as shown in FIG. 3(f) and provided to the other
input of adder-subtracter circuit 11.
Adder-subtracter circuit 11 accumulates respective pulses from
comparators 9 and 10 to output a signal indicating any one of the
three statuses of-1, 0, +1 obtained each time, as shown in FIG.
3(g), as an output signal of two bits. Similar to the RF signal,
the output signal is provided to a demodulation circuit not shown
to be subjected to the general demodulation process.
More specifically, adder-subtracter circuit 11 operates (in the
example of FIG. 3, adding operation including the polarity thereof
is carried out) on the pair of pulse strings ((e) and (f) in FIG.
3) obtained by binarizing TPP signals by comparators 9 and 10.
Based on the operation result, the two statuses of -1 or +1 can be
restored according to the pit depths in the pit portion (more
specifically, the generation sequence of positive and negative
pulses based on the TPP signal), and the one status of 0 can be
restored in the non-pit portion. Therefore, information of a total
of three values can be recorded and reproduced depending upon the
absence/presence and the depth of the pit. As a result, the
recording density of information on an optical recording medium can
be improved significantly as compared with the conventional
so-called binary recording.
In the user region of the disk, a reproducing operation similar to
that of the conventional binary recorded information is to be
carried out since all the pits have the same depth (D1). Referring
to FIG. 3(c), in the pit of depth D1, a positive TPP signal and a
negative TPP signal are generated when the beam spot is located at
the leading edge and trailing edge of the pit, respectively. By
adding the pulses, including the signs, of (e) and (f) of FIG. 3
that are obtained by binarizing these positive and negative TPP
signals using adder-subtracter circuit 11, a signal of the two
status of +1 at the pit portion and 0 at the non-pit portion can be
obtained. Therefore, in the reproduction method and reproduction
apparatus of the first embodiment of the present invention, the
region having the main information recorded according to pits of
the same depth, i.e. the user region, can have binarization
information restored and reproduced. The region having another
information recorded according to pits of different depths, i.e.
the lead-in region, can have three-valued information restored and
reproduced. The same reproduction method can be used for either
region.
As to the region having the main information recorded according to
pits of the same depth, i.e. as to the user region, the
binarization information may be reproduced based on only a
reproduced RF signal as in the conventional case. In this case, a
conventional circuit can be used for the reproduction circuit of
the main information. As a result, the cost of the reproduction
apparatus can be reduced.
Thus, in the lead-in region of the optical recording medium
according to the first embodiment of the present invention,
information is recorded at least in the depth direction, or in the
depth direction in addition to the plane direction of the substrate
(conventional binary recording). Therefore, more information can be
recorded in the lead-in region than in the conventional ROM disk
that has information recorded only in the plane direction. As a
result, a usable region can be preserved or expanded even if the
amount of information recorded in the lead-in region is
increased.
Furthermore, copyright protection can be effected by recording
information in the depth direction in the lead-in region. This will
be described in detail hereinafter.
As described in relation to the conventional example of FIG. 13,
the polarity of the TPP signal obtained from the user region of a
recordable disk is identical for all marks 55 as shown in FIG. 13D
since marks 55 all have the same depth in the user region.
Therefore, the information recorded in the depth direction (ternary
recording) by pits 2a and 2b of different depths among the
information in the lead-in region of the ROM disk recorded as shown
in FIG. 1B will by no means be transferred to the user region (only
binary recording possible) of the recordable disk. In other words,
information in the lead-in region of the optical disk of the first
embodiment will never be copied into another recordable disk.
By scrambling or encrypting the information in the user region in
the optical disk of the first embodiment and recording the cancel
key thereof in the lead-in region using the depth direction, the
cancel key recorded in the lead-in region will by no means be
copied into another recordable disk even if the information in the
user region is copied into another recordable disk. This means that
the information in the ROM disk according to the first embodiment
of the present invention substantially cannot be copied.
It is to be noted that information unique to the disk such as disk
identification (ID) information other than the cancel key may be
similarly recorded in the depth direction of the lead-in region. By
such recording, undesirable copying of these information to a
recordable disk can be inhibited completely. In other words,
illegal copy of a disk that includes copyrighted contents can be
prevented.
Although the above-described first embodiment corresponds to the
case where information is recorded at least in the depth direction
of the lead-in region, it will be understood that the region where
recording is to be effected in the depth direction is not limited
to a lead-in region, and can be effected on any region of the
optical disk. More specifically, it is impossible to copy
information from a region where the information is recorded in the
depth direction to another recordable disk. Such a region can be
identified as a unique region (for example, the above-described
lead-in region) in the optical disk.
The above-described embodiment is directed to a transparent
substrate having a thickness of 0.6 mm and a refractive index of
1.5 using a light beam having a wavelength of 650 nm and an optical
system having an NA of 0.6. However, it is apparent that the
above-described effect is not limited to the type of the used
optical system, substrate or the like. Furthermore, the values of
the pit depths are not limited to those shown in the above
embodiment. According to the principle of the present invention, it
is clear that depths are to be selected so that the polarity of the
TPP signal differs for respective pits. Since a recordable disk
does not have a recording dimension in the depth direction, copying
information from an optical disk having a region recorded with
information in the depth direction according to the above-described
embodiment to a recordable disk can be inhibited. It is also
apparent that the specific method therefor is not limited to that
described above.
Second Embodiment
Referring to FIG. 4, an identify circuit of recorded information in
a reproduction apparatus of an optical recording medium according
to a second embodiment of the present invention will be described
with reference to FIG. 4. More particularly, FIG. 4 is a block
diagram showing the circuit configuration that allows detection of
the presence of pits from which a TPP signal of different polarity
can be obtained on the optical disk.
Similar to the reproduction apparatus of the first embodiment shown
in FIG. 2, the outputs from regions A and B of detector 6 are
provided to differential amplifier 7 and addition amplifier 8.
Similar to the first embodiment of FIG. 2, the TPP signal which is
the output of differential amplifier 7 is applied to comparators 9
and 10. The TPP signals binarized by respective comparators 9 and
10 are applied to a marker detection circuit 15. The RF signal
which is the output of addition amplifier 8 is provided to
comparator 14 to be compared with a predetermined reference value.
The RF signal binarized by comparator 14 is also applied to marker
detection circuit 15.
Marker detection circuit 15 determines whether there is a pit that
causes the polarity of the TPP signal to be inverted for respective
pits based on the binarization signals (FIG. 3(e) and (f)) output
from comparators 9 and 10 and the binarization signal (FIG. 3(d))
output from comparator 14.
By the output of marker detection circuit 15, determination is made
as to whether the optical recording medium subjected to
reproduction is a disk having a region in which information is
recorded in the depth direction. According to the second embodiment
of the present invention, the presence of pits of different depths
can be used as the so-called identification marker (ID) to identify
that optical recording medium.
Third Embodiment
A recordable disk as an example of an optical recording medium
according to a third embodiment of the present invention will be
described here with reference to FIGS. 5A-5D. FIGS. 5A and 5B
schematically show the structure of a mark string and pit string on
a recordable disk according to the third embodiment. FIGS. 5C and
5D represent the waveforms of signals obtained by reproducing the
information recorded on the disk.
In general, mark 25 is written in either or both of the groove and
land. The third embodiment of FIG. 5 corresponds to the example
where marks 25 are written in groove 24.
More specifically, FIG. 5A schematically shows mark strings 26
constituted by marks 25 formed in groove 24 and a pit string 23
constituted by pits 22a and 22b arranged between these mark
strings, illustrated in a linear version from the inner
circumference region to the outer circumference region of the disk.
FIG. 5B schematically shows the cross section of the disk
corresponding to mark string 26 and pit string 23 of FIG. 5A. Pit
string 23 formed in the lead-in region is constituted by relatively
shallow pits 22a (depth D1) and relatively deep pits 22b (depth
D2). More specifically, the third embodiment is different from the
conventional recordable disk shown in FIG. 13 in that the pits
forming pit string 23 are formed of two types of pits, i.e.
relatively shallow pits 22a and relatively deep pits 22b.
FIG. 5C shows an RF signal representing the quantity of reflected
light obtained by reproducing mark string 26 and pit string 23 with
a reproduction light beam. It is noted that the quantity of
reflected light of the mark portion and the pit portion is smaller
than the quantity of reflected light of the non-mark portion and
non-pit portion.
FIG. 5D represents a TPP signal obtained by reproducing mark string
26 and pit string 23 with a reproduction light beam. The polarity
of TPP signals obtained from mark 25 and relatively shallow pit 22a
are identical. Only the polarity of a TPP signal obtained from
relatively deep pit 22b is inverted. More specifically, by forming
the lead-in region with pits 22a and 22b of two different depths,
information can be recorded in the depth direction of a disk
substrate taking advantage of the positive and negative values,
that is, the polarity of the TPP signal, that are easy to
determine.
These two different pit depths D1 and D2 are to be set so that RF
signals of the same amplitude and TPP signals of different polarity
are obtained from pits 22a and 22b. More specifically, similar to
the first embodiment, depths D1 and D2 are to be set so as to
satisfy: .lamda./8n<D1<.lamda./4n and
.lamda./4n<D2<3.lamda./8n where .lamda. is the wavelength of
the light beam and n is the refractive index of the substrate.
As to a reproduction method and reproduction apparatus of a signal
from pit string 23 formed of pits 22a and 22b of two different
types of depth and mark string 26 formed of marks 25 are
substantially identical to those of the optical disk of the first
embodiment described with reference to FIGS. 2 and 3. Therefore,
description will not be repeated for the common elements.
More specifically, similar to the reproduction apparatus of the
first embodiment, the reproduction apparatus of the third
embodiment includes an adder-subtracter circuit 11 that applies an
operation on a pair of pulse signals (adding operation including
polarity) obtained by binarizing respective TPP signals by
comparators 9 and 10. Based on the results of the operation, the
two statuses of -1 or +1 can be restored according to the pit depth
in the pit portion. In the non-pit portion, one status of 0 can be
restored. Therefore, information of the total of three values can
be recorded and reproduced depending upon the absence/presence and
depth of the pit. As a result, the recording density of information
on the optical recording medium can be increased significantly than
by the conventional so-called binary recording.
According to the reproduction method and reproduction apparatus of
the third embodiment, the RF signal and TPP signal can be shared in
order to reproduce a signal from the mark portion. More
specifically, referring to FIG. 5D, a positive TPP signal and a
negative TPP signal are obtained when the beam spot is located at
the leading edge and trailing edge, respectively, for mark 25.
Therefore, similar to the reproduction apparatus of the first
embodiment shown in FIG. 2, by accumulating pulse signals (FIG.
3(e), (f)) obtained by binarizing the TPP signal at
adder-subtracter circuit 11, the two statuses of +1 at the mark
portion and 0 at the non-mark portion can be achieved. More
specifically, binarization information for the mark portion and
ternary information for the pit portions of different depths can be
respectively restored and reproduced in the present reproduction
method or reproduction apparatus of recorded information. The same
reproduction method can be applied for either region.
In the third embodiment of FIG. 5, the region where the main
information is recorded with pits of the same depth, i.e., the user
region, can have binarization information reproduced from only an
RF signal as in the conventional case. In this case, the
conventional circuit can be used for the reproduction circuit of
the main information. As a result, the cost of the reproduction
apparatus can be reduced.
Thus, since the lead-in region of the recordable optical disk of
the third embodiment of the present invention can have information
recorded at least in the depth direction, or in the depth direction
in addition to the substrate plane direction (conventional binary
recording), more information can be recorded in the lead-in region
than in the conventional recordable disk that records information
only in the plane direction. As a result, a usable region can be
preserved or enlarged even if the amount of information to be
recorded in the lead-in region increases.
By recording information in the depth direction in the lead-in
region. in the present third embodiment shown in FIG. 5, copyright
protection can be effected. This will be described in detail
hereinafter.
Since the depth of the recording marks in the recordable region
(user region) of the recordable disk of FIG. 5 is constant, the
polarity of the TPP signal is identical for all the marks as shown
in FIG. 5D. Therefore, the information recorded in the depth
direction by pits 22a and 22b of different depth of the recorded
information in the lead-in region of the recordable disk in FIG. 5B
will by no means be transferred to the user region of the
recordable disk. In other words, information in the lead-in region
of the optical disk of the third embodiment can never be copied to
another recordable disk.
By scrambling or encrypting the information in the user region in
the optical disk of the third embodiment and recording the cancel
key in the lead-in region using the depth direction as described
above, the cancel key recorded at the lead-in region will never be
copied even if the information in the user region is copied into
the another recordable disk. Therefore, copying information in the
recordable disk by the third embodiment is inhibited.
It is to be noted that information unique to the disk such as disk
identification (ID) information other than the cancel key may be
similarly recorded in the depth direction of the lead-in region. By
such recording, undesirable copying of these information to another
recordable disk can be inhibited completely. In other words,
illegal copying of a disk that includes copyrighted contents can be
prevented.
The above-described embodiment is directed to a transparent
substrate having a thickness of 0.6 mm and a refractive index of
1.5 using a light beam having a wavelength of 650 nm and an optical
system having an NA of 0.6. However, it is apparent that the
above-described effect is not limited to the type of the used
optical system, substrate or the like. Furthermore, the values of
the pit depths are not limited to those shown in the above
embodiment. According to the principle of the present invention, it
is clear that depths are to be selected so that the polarity of the
TPP signal differs for respective pits. Since a recordable region
(user region) of the above-described recordable disk is absent of a
recording dimension in the depth direction, copying information
from an optical disk having a region recorded with information in
the depth direction according to the above-described embodiment to
a recordable disk can be inhibited. It is also apparent that the
specific method therefor is not limited to that described
above.
Although the present invention has been described and illustrated
in detail, it is clearly understood that the same is by way of
illustration and example only and is not to be taken by way of
limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
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